Method to control the execution of a shift to a lower gear with a released accelerator pedal in a drivetrain provided with a dual-clutch, servo-assisted transmission

Abstract

A method to control the execution of a shift to a lower gear with a released accelerator pedal in a drivetrain provided with a dual-clutch, servo-assisted transmission; the following steps are provided: opening, in a first instant, an outgoing clutch; closing, in the first instant, an incoming clutch; completing the opening of the outgoing clutch with a first linear ramp in a second instant; synchronizing, between the second instant and a third instant, a rotation speed of the internal combustion engine with a rotation speed of the incoming clutch; closing of the incoming clutch with a second linear ramp starting from a fourth instant, which is prior to or coincides with the second instant; completing the closing of the incoming clutch in a fifth instant, which coincides with or is subsequent to the second instant; and activating the internal combustion engine so as to generate a torque between the fourth instant and the third instant.

The invention claimed is: 
     
       1. A method to control the execution of a shift to a lower gear with a released accelerator pedal in a drivetrain provided with a dual-clutch, servo-assisted transmission, so as to shift from a current gear to a following gear, which is shorter than the current gear; the drivetrain comprises a dual-clutch, servo-assisted transmission having two primary shafts; at least one secondary shaft connected to drive wheels; and two clutches, each interposed between a drive shaft of an internal combustion engine and a corresponding primary shaft; the control method comprises the steps of:
 opening, in a first instant, an outgoing clutch associated with the current gear; 
 closing, in the first instant, an incoming clutch associated with the following gear; 
 completing the opening of the outgoing clutch by means of a first linear ramp in a second instant; 
 closing the incoming clutch by means of a second linear ramp starting from a third instant, which is prior to or coincides with the second instant; 
 synchronizing, between the second instant and a fourth instant, a rotation speed of the internal combustion engine with a rotation speed of the incoming clutch, namely with the rotation speed imposed by the gear ratio of the following gear; 
 completing the closing of the incoming clutch in a fifth instant, which coincides with or is subsequent to the second instant; and 
 activating the internal combustion engine so as to generate a torque between the third instant and the fourth instant in order to increase the rotation speed of the internal combustion engine. 
 
     
     
       2. The control method according to  claim 1 , wherein the fifth instant coincides with the second instant. 
     
     
       3. The control method according to  claim 1 , wherein the fifth instant is subsequent to the second instant. 
     
     
       4. The control method according to  claim 1 , wherein the third instant is prior to the second instant. 
     
     
       5. The control method according to  claim 1 , wherein the third instant coincides with the second instant. 
     
     
       6. The control method according to  claim 1 , wherein a longitudinal deceleration of a road vehicle increases between the fourth instant and the fifth instant. 
     
     
       7. The control method according to  claim 1  and comprising the further steps of:
 detecting a preference of a driver; and 
 changing, based on the preference of the driver, an advance of the complete opening of the outgoing clutch relative to a complete transfer of the entire torque of the internal combustion engine to the incoming clutch. 
 
     
     
       8. The control method according to  claim 7 , wherein the advance of the complete opening of the outgoing clutch relative to the complete transfer of the entire torque of the internal combustion engine to the incoming clutch is variable between a minimum, when the outgoing clutch is completely opened in the fifth instant, and a maximum, when the outgoing clutch is completely opened in the fourth instant. 
     
     
       9. The control method according to  claim 1 , wherein the internal combustion engine is in cut-off condition before the shift to a lower gear and is in cut-off condition also after the shift to a lower gear. 
     
     
       10. The control method according to  claim 9 , wherein, before, during and after the shift to a lower gear, a driver keeps the accelerator pedal completely released. 
     
     
       11. The control method according to  claim 1  and comprising the further steps of:
 detecting a pressing of the accelerator pedal exerted by a driver during the shift to a lower gear; 
 increasing, in case the accelerator pedal is pressed by a driver during a shift to a lower gear, the torque generated by the internal combustion engine; and 
 accelerating, in case the accelerator pedal pressed by a driver during a shift to a lower gear, the closing of the incoming clutch.